- Person
- Stanley Cohen
- Lived
- b. 1935
- Field
- Genetics
- From
- American
The story
A successful gene-cloning experiment needs a carrier, known as a vector: a piece of DNA that can be opened, have new DNA inserted, and still copy itself inside a cell. In the early 1970s Stanley Cohen's laboratory at Stanford was studying plasmids, small rings of DNA that bacteria carry and share, many of which make bacteria resistant to antibiotics. One of his laboratory's plasmids, called pSC101, its name honouring the initials of its discoverer, turned out to be the ideal carrier.
pSC101 had two crucial features. Herbert Boyer's restriction enzyme EcoRI cut it at only one site, so it could be opened without destroying its ability to replicate. And it carried a gene that made E. coli resistant to the antibiotic tetracycline.
The first success of the Cohen-Boyer collaboration, in spring 1973, used exactly these features. The opened pSC101 DNA was mixed with other DNA cut by the same enzyme, and the matching sticky ends of the pieces joined together into new loops. Another enzyme sealed the joins, and the loops were introduced into bacteria treated with calcium chloride so that they would take up DNA. The bacteria were then spread on a culture containing tetracycline. Only those carrying the recombinant plasmids survived, so the new combinations could be picked out easily.
The plasmid served as the vehicle for the experiments, published in 1973 with Annie Chang and Robert Helling, that showed foreign DNA could be cloned and copied in bacteria. The team then joined tetracycline-resistance plasmids with plasmids carrying resistance to another antibiotic, kanamycin, and went on to clone DNA from another bacterial species, Staphylococcus, and from the African clawed frog, testing the resulting colonies for the frog's ribosomal RNA gene.
The idea of a vector with a single cutting site and a selectable marker became the template for the cloning tools that followed. The laboratory notebooks from this plasmid work, together with parts of the laboratory where it was done, are now held by the Smithsonian's National Museum of American History.
Why it matters
The design principles of pSC101, a single cutting site and a selectable marker, remain the basis of the cloning vectors used in laboratories everywhere.
About Stanley Cohen
Stanford geneticist who, with Herbert Boyer, invented recombinant DNA cloning in 1973, the technique that launched genetic engineering and the biotechnology industry.
More about Stanley Cohen
- Stanley Cohen co-invented genetic engineeringIn 1973 Stanley Cohen and Herbert Boyer first moved genes between organisms, inventing recombinant DNA, the technique behind human insulin and the biotechnology industry.
- Stanley Cohen helped build biotechnology in TaiwanBeyond his Stanford laboratory, Stanley Cohen helped develop research collaboration with Taiwan's Institute of Molecular Biology and a biotechnology industry in Taiwan.
- Stanley Cohen investigated how bacteria resist antibioticsStanley Cohen's genetic engineering grew out of a medical question: how bacteria share genes that make them resistant to antibiotics.
- Stanley Cohen built tools to watch genes at workAfter inventing DNA cloning, Stanley Cohen developed techniques that use reporter genes to follow how genes behave in the cells of animals and other complex organisms.
- Stanley Cohen backed a safety pause on gene splicingStanley Cohen signed the 1974 letter calling for a voluntary pause on some recombinant DNA experiments until their risks could be assessed, and took part in the 1975 Asilomar conference.
- Stanley Cohen taught bacteria to take up new DNAIn 1972 Stanley Cohen’s Stanford lab showed that a calcium chloride treatment lets E. coli take up plasmid DNA and pass it on to their offspring.
- Stanley Cohen's patent was licensed to hundreds of firmsThe Cohen–Boyer recombinant DNA patents were licensed non-exclusively, for moderate fees, to 478 companies, spreading gene cloning across the biotechnology industry.
Sources
- Herbert W. Boyer and Stanley N. Cohen Science History Institute
- Stanley Norman Cohen Wikipedia
- Stanley N. Cohen Papers: biographical note National Library of Medicine
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